iio: st_sensors: fix errorcheck for regulators

We were checking the return code of vdd when we should be checking
vdd_io. My mistake, mea culpa.

Cc: Giuseppe BARBA <giuseppe.barba@st.com>
Reported-by: Giuseppe BARBA <giuseppe.barba@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/common/st_sensors/st_sensors_core.c

@@ -247,9 +247,9 @@ int st_sensors_power_enable(struct iio_dev *indio_dev)
 	}
 
 	pdata->vdd_io = devm_regulator_get(indio_dev->dev.parent, "vddio");
-	if (IS_ERR(pdata->vdd)) {
+	if (IS_ERR(pdata->vdd_io)) {
 		dev_err(&indio_dev->dev, "unable to get Vdd_IO supply\n");
-		err = PTR_ERR(pdata->vdd);
+		err = PTR_ERR(pdata->vdd_io);
 		goto st_sensors_disable_vdd;
 	}
 	err = regulator_enable(pdata->vdd_io);